Advances in plasma processing have provided for growth in the semiconductor industry. During substrate processing, conditions of the chamber may impact substrate processing. A critical parameter that may affect the plasma processing of substrates is the flow of the radio frequency (RF) current.
To facilitate discussion, FIG. 1 shows a simple block diagram of a capacitively-coupled plasma processing system 100 with a processing chamber 102 having an adjustable gap. In an adjustable-gap processing chamber 102, a lower electrode, such as an electrostatic chuck 104, may be configured to be adjustable to enable a plasma, which may be created between an upper electrode 114 and lower electrode 104 (i.e., gap 106), to be modified as needed.
Consider the situation wherein, for example, RF current from an RF supply 108 flows through an RF match 110 into processing chamber 102 during substrate processing. The RF current may travel along a path 116 to couple with a gas reactant to create plasma for processing a substrate 112, which is disposed on electrostatic chuck 104.
Those skilled in the arts are aware that RF current flowing into the plasma processing system 100 usually tries to return to its RF source. However, the RF current may not flow along the intended path to return to its RF source. The uncontrolled flow of RF current back to its RF source may cause processing conditions to fall outside of the design window. In an example, uncontrolled flow of RF current may cause substrate 112 to experience non-uniformity during substrate processing and may result in a greater number of defective devices.
Since RF current tends to seek a path with low impedance, a low impedance path may be provided to direct the flow of RF current. One method of providing for a low impedance path is by employing a set of straps 118. In an example, eight straps may be symmetrically connected to electrostatic chuck 104 and/or the inner lining of processing chamber 102. The eight straps enable the RF current to flow out in a radial direction with respect to substrate 112, thereby minimizing non-uniformity and providing a more deterministic path for the RF current.
Since set of straps 118 is employed to provide a deterministic return path for the RF current, the integrity of the set of straps 118 needs to be maintained. In other words, the set of straps 118 has to be in good working condition to ensure that the deterministic path of the RF current is available. However, conditions may exist that may cause set of straps 118 to lose its integrity and create an inconsistent RF return impedance causing shift in wafer processing result.
As aforementioned, lower electrode 104 is elevated and lowered to modify the plasma created during substrate plasma processing. Since set of straps 118 is attached to electrostatic chuck 104, set of straps 118 is also configured to move along with electrostatic chuck 104. Over time, material fatigue (e.g., metal fatigue) may cause set of straps 118 to break (such as a tear in one of the straps). Once a break occurs in a strap, the cross-sectional area of the strap is changed, thereby increasing the impedance of the strap. As a result, the RF current may not flow as intended.
In another example, the connection between a strap of the set of straps 118 to lower electrode 104 and/or the inner lining of processing chamber 102 may break. As a result, the RF current may be altered.
Besides the aforementioned reasons, the design of a strap may also impact the strength, flexibility and durability of the strap. If the material that has been utilized to create the strap is poorly chosen, for example, the strap may not be able to withstand the corrosive plasma processing conditions or present a lossy current path affecting the efficiency of the power delivery system. Power loss due to poor choice of base material may heat up the strap and may cause premature failure.